In installing torque prevailing nuts of the type that are pre-crimped with the usual power tool or nut runner, it is possible to install an occasional nut which has either too little self-locking torque or none at all. To prevent such improper installation going unnoticed, a power installation tool is needed to immediately signal the operator that the nut has less locking torque than is acceptable. Such improper nut can then be removed and a proper one installed.